镍(II)配合物官能化的MCM-41催化分子氧环氧化苯乙烯

制备了镍(II)席夫碱配合物官能化的MCM-41多相催化剂MCM-41-Ni.利用X射线粉末衍射、氮气物理吸附脱附、红外光谱、热重、电感耦合等离子体原子发射光谱、元素分析和透射电镜等方法对催化剂进行了表征.以氧气为氧化剂,MCM-41-Ni在催化环氧化苯乙烯的反应中表现出较高的催化活性;苯乙烯的转化率为95.2%,环氧苯乙烷的选择性为66.7%.系统地研究了反应温度、催化剂用量、溶剂以及反应时间对反应性能的影响.催化剂经过4次循环仍然表现出较好的稳定性和催化活性.     

Assessment of porosities of SBA-15 and MCM-41 using water sorption calorimetry

Water sorption calorimetry has been used for characterization of 2D hexagonally ordered mesoporous silica SBA-15. Experimental data on water sorption isotherm, the enthalpy, and the entropy of hydration of SBA-15 are presented. The results were compared with previously published results on MCM-41 obtained using the same technique. The water sorption isotherm of SBA-15 consists of four regimes, while the sorption isotherm of MCM-41 consists only of three. The extra regime in the water sorption isotherm for SBA-15 arises from filling of intrawall pores, that are present in SBA-15 but absent in MCM-41. The water sorption isotherms of the two types of mesoporous silica were analyzed using the Barrett-Joyner-Halenda approach. For the BJH analysis, t-curves of silica with different degrees of hydroxylation were proposed. Comparison of water and nitrogen t-curves shows that, independent of hydroxylation of silica surface, the adsorbed film of water is much thinner than the adsorbed film of nitrogen at similar relative pressures. This fact decreases the uncertainty of the assessment of porosity with water sorption originated from variations in surface properties. The pore size distribution of SBA-15 calculated with BJH treatment of water sorption data is in good agreement with nitrogen NLDFT results on the same material.     

Sulfonated carbon catalyzed oxidation of aldehydes to carboxylic acids by hydrogen peroxide

Sulfonated carbon as a strong and stable solid acid catalyst exhibited excellent catalytic performance in various acid-catalyzed reactions. Here, sulfonated carbon, as catalyst for oxidation reaction, was prepared via the carbonization of starch followed by sulfonation with concentrated sulfuric acid. N₂ physisorption, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray fluorescence and acid-base titration were used to characterize the obtained materials. The catalytic activity of sulfonated carbon was studied in the oxidation of aldehydes to carboxylic acids using 30 wt% H₂O₂ as oxidant. This oxidation protocol works well for various aldehydes including aromatic and aliphatic aldehydes. The sulfonated carbon can be recycled for three times without obvious loss of activity.     

Styrene epoxidation over a SBA-15-supported Mn(III) Schiff-base complex

2,4-Di-tert-butyl-6-((E)-(propylimino)methyl)phenol as a Schiff-base ligand was immobilized onto an amino-functionalized SBA-15 through the reaction between di-tert-butyl-salicylaldahyde and the tethered amino group. The Mn(III) metal complex of the immobilized Schiff-base ligand was proven to be an active catalyst for the epoxidation of styrene withtert-butyl hydroperoxide as a terminal oxidant. The catalysts behaved as an oxidation catalyst in the epoxidation and could be used many times without structural degradation, leaching of active manganese species and significant activity loss. It has been concluded that the reversible redox cycles of the metal center play a key role during the epoxidation reaction, as well as in the reusability of the catalysts.     

Modification of MCM-41 and SBA-15 mesoporous silicas by imidazolium ionic liquids

MCM-41 and SBA-15 mesoporous molecular sieves are modified with imidazolium ionic liquid (IL) via both physical adsorption and covalent grafting. The considerable effect of IL grafting on the porous structure and the particle morphology of mesoporous supports is shown. The pore size of these supports is found to be a key parameter determining the possibility of loading IL into such support materials.     

Aza-Michael addition reactions between nitroolefins and benzotriazole catalyzed by MCM-41 immobilized heteropoly acids in water

MCM-41 supported heteropoly acids(HPAs) catalysts were synthesized,characterized and their catalytic activity was evaluated in an aza-Michael addition reaction between nitroolefins and benzotriazole in water at room temperature.50 wt% PW/MCM-41 showed the highest activity(up to 96% yield).The catalyst was used in six consecutive experiments without obvious loss of activity, confirming the success of the anchoring process and the catalyst stability.     

Efficient aerobic photooxygenation of aldehydes to carboxylic acids using cobalt(II) phthalocyanine sulfonate as a photosensitizer in organic-water biphasic media

Transition Metal Chemistry - The aerobic oxidation of a variety of aromatic aldehydes to the corresponding carboxylic acids by molecular oxygen in the presence of 4-carboxyl tetraphenylporphyrin...     

Hydrogen bonding of water confined in mesoporous silica MCM-41 and SBA-15 studied by 1H solid-state NMR

The adsorption of water in two mesoporous silica materials with cylindrical pores of uniform diameter, MCM-41 and SBA-15, was studied by 1H MAS (MAS=magic angle spinning) and static solid-state NMR spectroscopy. All observed hydrogen atoms are either surface -SiOH groups or hydrogen-bonded water molecules. Unlike MCM-41, some strongly bound water molecules exist at the inner surfaces of SBA-15 that are assigned to surface defects. At higher filling levels, a further difference between MCM-41 and SBA-15 is observed. Water molecules in MCM-41 exhibit a bimodal line distribution of chemical shifts, with one peak at the position of inner-bulk water, and the second peak at the position of water molecules in fast exchange with surface -SiOH groups. In SBA-15, a single line is observed that shifts continuously as the pore filling is increased. This result is attributed to a different pore-filling mechanism for the two silica materials. In MCM-41, due to its small pore diameter (3.3 nm), pore filling by pore condensation (axial-pore-filling mode) occurs at a low relative pressure, corresponding roughly to a single adsorbed monolayer. For SBA-15, owing to its larger pore diameter (8 nm), a gradual increase in the thickness of the adsorbed layer (radial-pore-filling mode) prevails until pore condensation takes place at a higher level of pore filling.     

Transformation of n- hexane on PtAl/MCM-41 and PtAl/SBA-15

PtAl/MCM-41 and PtAl/SBA-15 materials were prepared by post-synthesis alumination followed by introduction of platinum by ion exchange. The samples were characterized by pyridine adsorption followed by FTIR and TPR of hydrogen. The catalytic behavior was explored in the transformation of n-hexane. This revised version was published online in August 2006 with corrections to the Cover Date.     

Rapid water reduction to H2 catalyzed by a cobalt bis(iminopyridine) complex

A cobalt bis(iminopyridine) complex is a highly active electrocatalyst for water reduction, with an estimated apparent second order rate constant k(app) ≤ 10(7) M(-1)s(-1) over a range of buffer/salt concentrations. Scan rate dependence data are consistent with freely diffusing electroactive species over pH 4-9 at room temperature for each of two catalytic reduction events, one of which is believed to be ligand based. Faradaic H(2) yields up to 87 ± 10% measured in constant potential electrolyses (-1.4 V vs SCE) confirm high reactivity and high fidelity in a catalyst supported by the noninnocent bis(iminopyridine) ligand. A mechanism involving initial reduction of Co(2+) and subsequent protonation is proposed.     

Oxidation of thiols with molecular oxygen catalyzed by cobalt(II) phthalocyanines in ionic liquid

An efficient procedure for catalyst solubility, recycling and easy product isolation in oxidation of thiols to disulfides with molecular oxygen catalyzed by cobalt(II) phthalocyanines dissolved in ionic liquid at room temperature is reported.     

Carbonyl allylation of aldehydes and ketones with allylic chlorides catalyzed by immobilization of palladium in MCM-41

The heterogeneous carbonyl allylation of aldehydes and ketones with allylic chlorides was achieved in DMF using SnCl₂ as reducing agent at 25-40 °C in the presence of a 3-(2-aminoethylamino)propyl-functionalized MCM-41-immobilized palladium(II) complex [MCM-41-2N-Pd(II)], yielding a variety of homoallylic alcohols in good to high yields. This heterogeneous palladium catalyst exhibited higher activity than (N-propylethylenediamine)PdCl₂ and can be recovered and recycled by a simple filtration of the reaction solution and used for at least 5 consecutive trials without any decreases in activity.     

CuO and Ag2O/CuO catalyzed oxidation of aldehydes to the corresponding carboxylic acids by molecular oxygen

Furfural was oxidized to furoic acid by molecular oxygen under catalysis by 150 nm-sized Ag(2)O/CuO (92%) or simply CuO (86.6%). When 30 nm-size catalyst was used,the main product was a furfural Diels-Alder adduct. Detailed reaction conditions and regeneration of catalysts were investigated. Under optimal conditions, a series of aromatic and aliphatic aldehydes were oxidized to the corresponding acids in good yields.     

Magnetic ordering in a mononuclear cobalt(II) complex containing a Schiff-base pentadentate ligand

A mononuclear cobalt(II) complex CoL5, containing the pentadentate O2N3 salen-type Schiff-base ligand H2L5=N,N[prime or minute]-bis(3-tert-butyl-2-hydroxy-5-methylbenzylidenyl)-1,7-diamino-4-methyl-4-azaheptane, exhibits magnetic ordering at 4 K as proven by ac magnetic susceptibility (both in- and out-of-phase), magnetization, field-cooled magnetization and zero-field cooled magnetization measurements.     

CuCl catalyzed oxidation of aldehydes to carboxylic acids with aqueous tert-butyl hydroperoxide under mild conditions

Oxidation of aldehydes to the corresponding carboxylic acids can be performed highly efficiently at room temperature with 70% tert-butyl hydroperoxide (in water) in the presence of a catalytic amount of easily available ligand free CuCl in acetonitrile as solvent under very mild conditions. This oxidation protocol works well for various aldehydes including aliphatic aldehydes and aliphatic dialdehydes.     

Enthalpy and interfacial free energy changes of water capillary condensed in mesoporous silica, MCM-41 and SBA-15

The effect of confinement on the solid-liquid phase transitions of water was studied by using DSC and FT-IR measurements. Enthalpy changes upon melting of frozen water in MCM-41 and SBA-15 were determined as a function of pore size and found to decrease with decreasing pore size. The melting point also decreased almost monotonically with a decrease in pore size. Analysis of the Gibbs-Thomson relation on the basis of the thermodynamic data showed that there were two stages of interfacial free energy change after the constant region, i.e., below a pore size of 6.0 nm: a gradual decrease down to 3.4 nm and another decrease after a small jump upward. This fact demonstrates that the simple Gibbs-Thomson relation, i.e., a linear relation between the melting point change and the inverse pore size, is limited to the range not far from the melting point of bulk water. FT-IR measurements suggest that the decrease in enthalpy change and interfacial free energy change with decreasing pore size reflect the similarity of the structures of both liquid and solid phases of water in smaller pores at lower temperatures.     

Tetrapropylammonium perruthenate catalyzed glycol cleavage to carboxylic (di)acids

A new method to accomplish glycol cleavage to carboxylic (di)acids in one step using catalytic amounts of tetrapropylammonium perruthenate (TPAP) together with N-methylmorpholine N-Oxide (NMO) as the stoichiometric oxidant is presented. In addition to regenerating the active catalyst, the N-oxide stabilizes intermediary carbonyl hydrates and thereby shifts a crucial equilibrium. The mild oxidation protocol is applicable to a broad range of substrates providing the respective acids, diacids, or keto acids in high yields.